Sounds like a hardware fault. Keyboard reset is a hardware reset, software cannot crash so bad this doesn't work. The only reason this can happen is if the accelerator has overheated or something like that.

This is not exactly a hardware fault. Very bad crashes do that on my B1230 as well, and it's because of its maprom option : the rom, as copied in the ram, isn't write protected (write to $4FF80000 if you don't believe me) and bad crashes altering it, will force me to shut the power off. You may also get a red screen with a blinking led if the rom is just lightly altered (rom checksum error).
But if the rom (the space in ram where the rom got copied at first boot - but not at next ones !) is destroyed, the keyboard reset will still work but the machine won't reboot.